Isolation transformer upgrade for old guitar amps

Step 5 Illustrating the issues via schematics

Here's a schematic for the amp (complements of Paul Marossy's website.)

It's very typical of this amp type. Note the following:

-- the lack of a power transformer.
-- no fuse in the circuit.
-- the 35w4 diode is directly connected to the mains.
-- the GNDs are directly connected to the mains (this one doesn't even have the protection of a "death cap!")
-- the tube filaments are all connected in series, directly to the mains.

How do we fix it?

-- add an isolation transformer
-- add a fuse
-- reroute the ON/OFF switch
-- add a three-prong cord, and a proper earth ground

One issue will be dealt with later: using an iso transformer with a half-wave rectification circuit.